Process for concentrating dilute nitric acid.



E. COLLETT.

PROCESS FOR GONGENTRATING DILUTE NITRIC ACID.

APPLICATION FILED 001:.13, 1913.

1 1 38,%@, Patented Mar. 30, 1915.

min. contnrr, or 1:

TIANIA, NORWAY, ASSIGNO'R T0 NURSE HYDRO-ELEK'EIRISK KVAMSTOFAKTIESELSKAB, 01F CHRISTIANIA, NORWAY.

PROCESS FOR CONCEN'IMIING DILUTE NITRIQ ACID.

To all whom it may concern Be it known that T, EMIL Connnr na subject of the King of Norway, residing at Christiania, Norway, have invented certam new and useful Improvements in Processes for Concentrating Dilute Nitric Acid; and T-do hereby declare the following to be a full, clear, and exact descriptionof the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawings, and to letters or figures of reference marked thereon, which form a part of this specification.

In various industries large quantities of dilute nitric acid are obtained for instance by electric om'dation of the nitrogen of the air. Many methods have been tried to concentrate this dilute acid, for instance, by adding inert water binding substances; the nitric acid was then expelled in concentrated form by heating. As far as is b own, however, this problem has not been solved in an economically satisfactory manner.

The difiiculty consists in obtaining the dilute acid concentrated-up to about 60-.

70% without the use of the water-attracting agents. With an acid of this concentration a highly concentrated nitric acid is readily produced in a well known manner. As is known, nitric acid of a lower concentration than 68% is concentrated by boiling, the

vapors being not of the same composition as the boiling acid, before the said concentration has been reached. However, a dilute nitric .acid is dificult to concentrate economically by simply boiling it, and as a large proportion of the acid passes away with the vapors the output of concentrated acid is therefore very slight.

Applicant has found that dilute nitric acid may be very conveniently concentrated when proceeding in. the manner hereinafter described reference being had to the accompanyin drawing, which is a diagrammatic view 0 one form of apparatus for carrying out the present process.

In said drawing, 1, 2, and 3 designate three apparatuses ior' concentrating nitric acid by boiling; a, 5, and 6, the pipes through which the acid vapors, escaping from the evaporation apparatus, pass into a dephleg mation column 8, 9, 10, and 1i designate pipesthrough: which, acidin a liquid state flows back from Specification of Letters iPatent.

Application filed October 13, 1913. Serial No. 794,936.

.ratus (2),

mixed with nitric acid vapor. When the dephlegmation column into the concentration apparatus.

12 is a pipe for the escape of vapors from the dephlegmation column.

16 and 17 are pipes connecting the concentration apparatus.

Patented Mar. 30, 19115.

18 is a pipe through which water or dilute acid may be supplied to the dephlegmation column.

19 is a pipe through which the acid to be concentrated may be introduced into the dephlegmation' column. 7

The dilute nitric acid is boiled in the evaporating apparatus (1) which is made of an acid proof material. The vapors escaping are conducted to the fdephlegmation column 7, whereby they are separated into aqueous vapor and concentrated acid. The aqueous vapors will escape and the acid flow back to obtained a concentration of about 65-70%, the quantity. supplied and discharged is so controlled that the concentration of the acid will remain constant. While this method of concentration, according to circumstances, may be of advantage it has, however, the drawback that the dephlegmation column is highly charged with concentrated acid vapor which again necessitates making the column very large. Toalso avoid this inconvenience the following, process may be employed. The nitric acid is heated in a suitable concentrating apparatus (1) until boiled; the acid is allowed to boil in this apparatus'until the concentration has gone up from, for instance, 30 to 40%. The vapor escaping in this stage of c'encentration is relatively low in nitric acid and acot'dingly mainly consists of aqueous vapor. "After the desired concentration has been obtained, the acid is conducted-to another similar appain which the evaporation of the water is continued; in this apparatus the concentration is carried on, for instance, from 4.0 to 50%.; the aqueous vapor, escaping during this stage ofconcentration, is the de-. sired concentration has been obtained, the acid is further conducted to a similar apparatus (3) in which the concentration is carried'on or instance up to about -68%. The vapors escaping during this stage of the concentration are high in nitric acid. 9i" course the concentration may be efi'ected in more stagesthan herein mentioned.

The vapors issuing from the concentrating apparatus (at 4. 5 and 6 respectively), in order to extract the nitric acid contained in the same, are conducted to one or more dephlegmation columns (7), in which the vapors are subjected to dephlegina-tion in a known manner. The nitric acid delivered from the dephlegmation column (at 8) is again supplied tothe concentration apparatus at a'suitable point (at 9, 10 or 11 respectively). The-vapor issuing from the dephlegmation column, (at 12) under normal conditions,consists of nearly'pure water which for instance, after condensation, may again be used to absorb nitrous gases for the production of nitric acid, etc. The vapors are very advantageously introduced from the various-concentrating apparatus into the dephlegmation columns at points located-one above the other (at 13, 14 and l5 respectively)- the most concentrated vapors being introduced at the bottom and the more dilute ones at a higher point of the column. The aqueous vapor issuing from the first concentrating apparatus may also be separately condensed and again used in the apparatus in which the dilute nitric acid is produced It is thus also possible to separate a large proportion-of the vapor containing small quantities of nitric acid, and a comparatively small proportion containing a larger quantity of nitric acid. By means of the said dephlegmation column these vapors may then be separated into their components so as to eventually obtain, as already mentioned, only concentrated nitric acid and pure or nearly pure water. 0f

course the apparatus preferably operates continually the acid flowing from one apparatus to the other (at 16 17).

It is of great advantage to supply the dilute acid at the top of the dephlegmation column, a heating of the acid being thereby obtained which again increases the efiicien'cy of the apparatus. To obtain the best dephlegmation possible a dilute acid or water,

may be added to the dephlegmation'column (at-18) in suchja quantity as to obtain a practically complete dephlegmation. The upper limit-of the acid concentration has been found to .be at about 15-20%. H therefore an acid of this concentration 'be added, practically only aqueous vapor will escape from the top of the column.- Since, as already mentioned, it is advantageous to also add the. acid, that is to be concentrated, inthe dephlegmation column, this may convenientlv be done by-introducing-the same (at 19) somewhat below the point (18) at which-the said dilute acid or water is added."

Through the evaporation by steps, the great advantage obtained is that, the removal of most ofthe water is e'flected at a comparatively low concentration of the acid, consequently the evaporating apparatus, in which ncense the bulk of the water is evaporated, may be constructed for the corresponding low temperature and pressure, or the apparatus, at equal pressure and temperature of the vapor, will obtain a materially greater effi ciency. Moreover the process has the advantage of obtaining on one hand substantially all the nitric acid of the desired concentration, and on the other hand substantially pure aqueous vapor. Heretofore it has not been possible to accomplish this by any of the known processes. I

I claim:

1. The process of concentrating dilute nitric acid which comprises, evaporating the acid in stages of difierent concentrations, dephlegmating and condensing the resulting acid vapors while permitting the escape of aqueous vapor, and returning the condensed vapors to one of the stages.

2. The process of continuously concentrating dilute nitric acid which comprises, evaporating acid in stages of difierent concentrations, dephlegmating and condensing the vapors resulting from the several stages while permitting the escape of aqueous vapor from the vapor of a lower stage, returning the condensed vapors from all the stages to one of the lower stages, and maintaining a constant flow of concentrates from the lowest to the highest stage.

3. The process of concentrating dilute nitric acid which comprises, evaporating the nitric acid which comprises, evaporating the acid in stages of difi'erent concentrations, dephlegmating and condensing the resulting acid vapors in the presence of a nitric acid absorbing liquid while permitting the escape of aqueous vapor, and returning the condensed vapors to one of the stages.

6. The process of concentrating dilute nitric acid which comprises, evaporating the acid in stages of difierent concentrations, de-

phlegmating and condensing the resulting acid vapors'in the presence of weak acid while permitting the escape of aqueous vapor, and returning the condensed vapors to one of the stages.

7. The process of continuously concentrating dilute nitric acid which comprises, evapniaaeao orating acid in stages of difierent concentrations, dephlegmating and condensing in the presence of weak nitric acid, the vapors resulting from the several stages while permitting the escape of aqueous vapor from the vapor of a lower stage, returning the.

condensed vapors from all the stages to one of the lower stages, and maintaining a constant flow of concentrate from the lowest to the highest stage.

8. The process of continuously concentrat-' ing dilute nitric acid which comprises, evaporating acid in stages of difierent concentrations, dephlegmating and condensing in the presence of weak nitric acid, the vapors remy invention, l have signed my name in 25 presence of two subscribing witnesses.

. EMIL COLLETT.

Witnesses:

M. E. GU'rroRnNsEN, RUTH Lmns'rnom. 

